(1) Field of the invention
The invention relates primarily to a device for programmed spot treatment of a body with a beam of rays, using a lens system, in which the point of impact of the beam of rays describes a predetermined pattern on the surface of the body as a result of a movement which the body and the device carry out relative to each other.
(2) Description of the prior art
An example of such a device is described in DRG patent specification No. 241,567. This reference discloses a device for the treatment of a cylindrical clamped screen printing stencil with a laser beam. The screen printing stencil comprises a perforated sheet or a stencil gauze the perforations of same being sealed by means of a sealing agent such as a lacquer. The stencil is then treated in a programmed manner with a laser beam, so that the perforations being struck by the laser beam are stripped of their lacquer, and a cylindrical printing plate is formed in this way.
However, the invention is not limited to the type of device as described in the above-mentioned reference. In general, the invention relates to devices in which a particular treatment can be carried out on a body with a beam of rays. Examples are: exposure of a clamped film material, photo-curing of a clamped photopolymer material etc. Nor need the beam of rays used be limited to laser light; other light beams which have to be focused for efficient working also fall within the scope of the disclosure of the device according to the invention.
The body on which the beam acts will often be cylindrical; but a flat shape can also occur.
Such known devices have the disadvantage that the effect of their action is very sensitive to even very minor change in the distance of the lens to the surface of the body, since only the optimum action of a laser beam burning away, for example, lacquer is obtained if the focal point of the lens used remains on the surface of the body to be treated with radiation, or so far below said surface as is desirable in connection with the effect to be obtained. A consistently correct distance is, however, not simple to achieve, due to faulty settings and inaccuracies which may occur, including rotational and surface displacement inaccuracies.